iMessage & FaceTime 'Activation Unsuccessful' & Constant 'Verifying...'!

Hi all

I am completely exasperated with this issue now and just getting nowhere.

Since having a new iPhone 13 Pro Max on Sunday I have been getting the constant error message in iMessage and FaceTime 'Activation Unsuccessful' and when drilling down the mobile number constantly has 'Verifying...' next to it.

I have tried the following so far:

1. Turned iMessage and FaceTime off, turned the handset off, powered back up and re-enabled iMessage and FaceTime.
2. Gone to 'Phone' in Settings and re-typed the mobile number and saved it.
3. Reset the network settings, turned the handset off and powered back up.
4. Erased all content and settings and set handset back up.
5. Removed, cleaned and re-inserted the SIM.
6. Signed out of iCloud and then back in again.

I can send and receive SMS messages no problem.

Spoke to Apple support who seem to be at a loss as well and said it's an issue with the SMS with the network (EE). I don't see how as I am sending and receiving SMS messages no problem at all.

Anyone else had this issue and can shed some light on it or any further suggestions would be very much appreciated.